they built a lot of 4 speed chargers ,just as they built 4 speeds in many other performance cars back then,its possible if you can find the parts to do it with,i used to have a 68 charger r/t with 4 speed in it,and it wont cost you an arm and a leg to do it either ,there's guys around with the right parts to do that one with,it should cost you around 800-1000 buck tops,good luck.